Most of the terrorists involved in the Madrid train bombings (search) are in jail, but contrary to previous government claims, some of those who planned the attacks probably are not, former Interior Minister Angel Acebes (search) told a parliamentary commission Wednesday.

Acebes said the commission, which is investigating the circumstances of the bombing that killed 191 passengers and bystanders, should focus on who decided the date of the attack — three days before general elections that gave an unexpected victory to the Socialists, who had promised to withdraw Spain's troops from Iraq.

"The pieces don't fit," Acebes told the commission. Investigators need to learn "who planned the attack ... who programmed in detail the precise succession of events in those hours ... who planned the sequence of leads, especially the day and the hour of claiming responsibility of the attack the afternoon" before the March 14 general elections, Acebes said.

Islamist militants with possible links to Al Qaeda (search) are blamed for planting 10 backpack bombs on four commuter trains, also wounding some 1,600 people. Of 50 people arrested, 16 remain in jail, including two believed to have put explosives on the trains. Most are Moroccan.

Spain's two main parties bitterly dispute any connection between the attack and the election outcome. Socialists claim they would have won anyway. The opposition disputes that, implicitly calling into question the legitimacy of the current government of Prime Minister Jose Luis Rodriguez Zapatero (search).

The government stated weeks ago that it thought the core group of bombers were in custody.

Acebes spoke as the commission neared the end of three-day-a-week hearings that began July 6. After Thursday's session the group was to recess and return in late August or early September, then debate in Parliament recommendations to improve the country's security against future attacks.

Later Wednesday, former foreign minister and current parliamentary deputy Ana Palacio (search) was to testify. She was expected to face questions including why her ministry initially told other governments the attackers were the Basque separatist group ETA, when police almost from the first day were focusing on an Islamic connection.

Critics claim the Popular Party did that to shield themselves from an expected voter backlash if the attack seemed to relate to former Prime Minister Jose Maria Aznar's (search) support for last year's U.S.-led invasion of Iraq and subsequent deployment of 1,300 troops to the military occupation.

The accusation comes from former opposition parties including the Socialists now in government and smaller groups that dominate the 16-member commission investigating the March 11 bombing.